The present invention relates to an endoscope, and more particularly, to an endoscope which is capable of indicating an actual size of an object being observed, a magnification of an objective optical system, a distance to the object being observed and the like in a visual field.
By way of example, an endoscope having an actual size indicator is disclosed in Japanese Patent Publication No. Sho 49/1974-44752. This endoscope has been known as the one which is capable of measuring an actual size of an affected part within a coeliac cavity or of an object being observed such as a foreign substance.
The endoscope just described produces an electrical signal corresponding to a relative movement between an objective lens barrel which is movable along its optical axis to make a focus adjustment and an image transmitter which faces one end of the objective lens barrel and cooperatively moves a measure indicator disposed at a light exit end portion which is the other end of the image transmitter in response to the electrical signal to allow an indication of a length in the measure indicator to vary in proportion to the relative movement.
However, the endoscope includes a potentiometer at its distal end portion which potentiometer comprises a resistor and a slider which moves in cooperation with and in proportion to movement of the objective lens barrel and a d.c. instrument having a rotor in an eyepiece portion of the endoscope. In addition, the endoscope has a wiring in its insertion portion which wiring electrically connects the potentiometer to the d.c. instrument. Consequently, devices specific to the endoscope have to be built in each portion thereof with the result of complication in structure.
U.S. Pat. No. 3,730,632 discloses an endoscope having a shading plate which is ganged with an objective lens barrel and transmitting a position of the shading plate through a light conductor to a measure indicator as a light signal to allow a length of a bright or a shaded area in the measure indicator to vary so that an actual size of an object being observed can be measured based on the variation of the length.
However, the foregoing endoscope only utilizes an optical means in place of the electrical means in the endoscope of the above-mentioned Japanese patent. As a result a light conducting member has to be further through a distal end portion, an insertion portion and a proximal operation portion of the endoscope in addition to an image transmitter which transmits an image of an object being observed, resulting in complication in structure. In addition, the measure indicator is disposed adjacent to an image exit end plane of the image transmitter and hence it is impossible to make the measurement by superposing an index on an image of an object being observed so that accuracy in the measurement may be limited.